This application is related to U.S. application Ser. No. 18,382 filed Mar. 7, 1979.
This invention relates to a combination tool which can both drill a hole and, with minor modification, drive a self-tapping fastener into that hole.
Tools of this general type have been disclosed in commonly owned U.S. Pat. Nos. 3,965,510 and 4,107,800 which disclosures are hereby incorporated by reference. In each of those patents, a drill bit is retained in a mandrel by means of a setscrew. The mandrel has a stem portion which may extend from, or be telescopically received in, a sleeve. The sleeve has a fastener-engaging socket on the end opposite to that from which the stem projects. When the stem is in the forward position, it is contained within the sleeve and the drill bit is in its projecting or operative position. When the stem is in its rearward position, the drill bit is withdrawn into the sleeve and the socket is foremost such that it can engage and drive a fastener.
These combination tools have proved highly successful for most drilling and driving applications. However, certain limitations of these tools render them not entirely suitable for certain applications. More specifically, these tools are not well suited for use with the high-powered rotary hammer which is capable of both rotational and percussive driving. When subjected to the high vibration of such a driver, the setscrews which retain the drill bits in the above mentioned combination tools tend to vibrate loose, regardless of the amount of torque used to tighten them.
A further problem with these tools occurs with the larger drill sizes which, coincidentally, require the high powered tools to drive them and their corresponding fasteners. For every inch of length added to the drill bit, roughly two inches must be added to the tool, one inch to the sleeve and one inch to the stem which must reach through that sleeve. For the larger fastener sizes, this means the portion of the stem received in the driver is a substantial distance from the fastener-engaging socket and, even farther yet from the tip of the fastener which is penetrating the material. This means the tool itself is subjected to increased rotational and longitudinal bending torques and the fastener is subjected to a greater risk of canting or misalignment.